Summary: Hydrothermal Systems as Indicators of Paleoclimate: an Example from the Great Basin, Western North America
G.B. Arehart
S.R. Poulson
University of Nevada, Reno; Reno, Nevada, USA
ABSTRACT: Many hydrothermal systems are dominated by water of meteoric origin, the stable isotopic
composition of which is, in part, a function of climate extant at the time the hydrothermal system was active.
Therefore, measurement of stable isotopic parameters in fossil hydrothermal systems provide a signal averaged
over relatively large time scales that potentially can yield insights into longer-term climate changes. Two
excellent indicators of the H isotope composition of meteoric waters from hydrothermal systems include fluid
inclusions and hydrous minerals. In the Great Basin of western North America, hydrothermal systems have been
active intermittently since at least Jurassic time. Data from the last half of the Tertiary in the Great Basin
correlate well with existing data from weathering-related minerals of known age (e.g. alunite, kaolinite) and
parallel global paleoclimate curves. A few data exist for older hydrothermal systems and can be utilized to
constrain meteoric water back to the Jurassic, but with relatively large uncertainties. Additional data are required
to better define this older portion of the secular curve for the Great Basin.
1 ORIGIN AND ISOTOPIC COMPOSITION OF
METEORIC FLUIDS
The stable isotopic composition of meteoric fluids has
been shown to reflect a number of parameters,
including differences in paleolatitude, differences in